The x-ray technology used in CT imaging is an important technology in medical imaging.
FIG. 1 shows, in an example manner, the setup of a modern so-called dual source CT system; however, embodiments of the invention are not restricted thereto.
Such a CT system 1 comprises a first x-ray tube or x-ray radiation source 2 with a detector 3 opposite thereto and a second x-ray tube 4 with a further detector 5 opposite thereto, wherein x-ray source and detector are arranged in such a way that a patient 7 to be penetrated by x-ray radiation can be placed between the two. The two x-ray radiation source and detector systems 2, 3 and 4, 5 are arranged in a gantry housing 6 on a gantry, which rotates about a system axis 9 and is not visibly depicted here. The patient 7 is situated on a longitudinally displaceable patient couch 8, which is pushed continuously or in a step-by-step manner through an opening in the gantry housing 6 for the purposes of scanning the patient 7 during the rotation of the x-ray radiation source and detector systems. As a result of this, the patient 7 is scanned in a helical or multiple circular manner, wherein x-ray radiation generated by the x-ray source penetrates the patient and is registered after the penetration thereof at a detector.
A control and computer unit 10 having computer programs and program modules Prgx, which are loaded and worked through as required during operation, in the memory 11 thereof serves to control the CT system 1. The control itself and the readout of detector output data is brought about by means of the control and data line 12, which connects the control and computer unit 10 with the gantry housing 6.
CT technology and, more generally, medical x-ray diagnostics ultimately are based on the fact that the object to be imaged, e.g. a patient 7, is penetrated by x-ray beams and that, in the process, the x-ray radiation is locally attenuated in terms of its intensity. Measuring the attenuation of the x-ray radiation allows conclusions to be drawn in respect of the object to be imaged. The attenuation to be measured emerges by way of the radiation intensity which the x-ray detector registers when the object is present compared to the radiation intensity that would be registered without the presence of the object.
If the x-ray radiation source is not stable in time and if it emits x-ray radiation that varies in terms of the intensity thereof, then the detector would detect different radiation intensities over time, even without the presence of an object. It is possible to measure the radiation intensity emitted by the x-ray radiation source by means of a so-called radiation monitor. Then, this measured value can be used in the evaluation of the detector signals.
A radiation monitor for x-ray radiation, used for this purpose, is a device including at least one sensor that can measure the intensity of x-ray radiation. The sensor (which is also referred to as a radiation monitor element) is introduced into the region irradiated by the x-ray radiation. Depending on the measured radiation intensity, the radiation monitor emits a signal which, for example, can be indicated, used for controlling the radiation generation process and used in the processing of the signal data from the detector. Here, a radiation monitor is generally configured in such a way that it is not situated in the region of the radiation field provided for determining the attenuation through the object, but rather situated in a different region of the radiation field which, however, is characteristic for the whole radiation field in terms of the properties registered by the radiation monitor.